Add conditional-4.vim

https://www.w3.org/TR/2020/WD-css-conditional-4-20200303/

Author: hail2u

after/syntax/css/conditional-4.vim

@@ -79,7 +79,11 @@
   display: revert;
 }
 
-@import "test.css" supports(display: auto);
+@import "conditional-3.css" supports(display: auto);
+
+@supports (selector(.conditional-4)) {
+  display: auto;
+}
 
 .color-3 {
   display: auto;